Constraints on the speed of sound in the k-essence model of dark energy

Abstract

We consider a k-essence scalar field model for the late-time cosmic acceleration in which the sound speed, parametrized as cs is constant. We compute the relevant background and perturbation quantities corresponding to the observables like cosmic microwave background, type Ia supernova, cosmic chronometers, baryon acoustic oscillations, and the fσ8. We put constraints on the cs2 parameter from these observations along with other parameters. We find lower values of cs2 which are close to zero are tightly constrained. Particularly, we find mean value of log10(cs2) to be -0.61 and cs2≤10-3 is more than 3σ away from this mean value. This means these observations favor a homogeneous dark energy component compared to the clustering one.